Method, resin and catalyst for increasing the tensile strength and core hardness of a sand mold or core

ABSTRACT

The tensile strength and core hardness of a sand mold or core is increased by incorporating into a mixture of a thermosetting acid-hardenable resin and sand, a dialkyl ester of the formula: 
     
         R.sub.1 OOC(CH.sub.2).sub.n COOR.sub.2 
    
     wherein R 1  and R 2 , which may be the same or different, are selected from alkyl of 1 to 20 carbon atoms and n is 2, 3 or 4. The ester may be added directly to the resin or sand, or in conjunction with the acid catalyst. Ferric chloride together with the dialkyl ester provides a sulfur-free catalyst for polymerization of the resin.

This is a division of application Ser. No. 809,546 filed June 23, 1977.

BACKGROUND OF THE INVENTION

Sand molds and cores are conventionally employed in the foundry industryfor the production of precision castings. These mold or cores aregenerally composed of sand particles bonded together with a resinbinder.

A wide variety of techniques have been developed for the manufacture ofsand molds. Generally, these techniques involve the use of thermosettingacid hardenable resin binders for the sand particles in order to formmolds or cores having the requisite surface hardness smoothness,strength and gas permeability so as to produce precision castings.

One method which has found widespread use in producing sand molds andcores involves heating a patterned mixture of sand and a thermosettingresin at a temperature generally ranging from 300° F. to 600° F. for aperiod of time sufficient to melt or polymerize the resin and thereforeproduce the desired mold or core (i.e. the hot-box or shell methods).Such processes are described by Brown et al, U.S. Pat. No. 3,020,609 andDunn et al., U.S. Pat. No.3,059,297 (each of which is incorporatedherein by reference in its entirety).

A particular disadvantage of the so called "shell" method resides in thehigh cost of the resin coated sand needed. Furthermore, both the shelland hot-box methods require heating of the pattern boxes to temperaturesof from 300° F. to 600° F. for periods of time which results in aconsiderable consumption of energy and fuel which with todays evergrowing energy crisis renders such techniques economically unattractive.

More recently, methods have been devised which eliminate the necessityof polymerizing the sand/resin mixture at elevated temperatures. Thesenew methods, commonly referred to as "no-bake" or "cold-box" techniques,generally involve the use of an acid catalyst to polymerize thesand/thermo-setting resin mixture. The acid catalyst may be in liquid,solid or gaseous form. Such processes are described by Blaies, U.S. Pat.No. 3,008,205; Dunn et al., U.S. Pat. No. 3,059,297; Peters et al., U.S.Pat. No. 3,108,340; Kottke et al., U.S. Pat. No. 3,145,438; Brown etal., U.S. Pat. No. 3,184,814; Robins, U.S. Pat. No. 3,639,654;Australian Pat. No. 453,160 and British Pat. No. 1,225,984, the entirecontents of each of the foregoing being incorporated herein by referencein its entirety. Many of these processes involve the use of sulfurcontaining acid catalysts such as benzene sulfonic acid, toluenesulfonic acid and the like.

When using the "no-bake" or "cold-box" methods, foundrymen generallyfind the resulting mold or core to exhibit a low tensile strength,thereby necessitating the use of undesirably high amounts of resin toattain satisfactory strength and core hardness. Use of higher suchamounts of resin is not only costly but provides a less satisfactorycasting.

While such "no-bake" or "cold-box" methods provide a more efficientmeans of producing sand molds and cores, there is ever present thedesirability of increasing the tensile strength and core hardness ofsuch products. Likewise, in view of the relatively short cure time ofsome sand/resin/acid catalyst systems, it is desirable to increase theworking time (i.e. mixing, mulling and depositing in mold or coreforming cavity) of the sand/resin/catalyst mix.

In addition, some difficulty has been experienced by foundrymen inmaintaining good steel strength qualities with precision steel castingsmade from sand molds or cores produced using a sulfur containingcatalyst. With a no-bake process using a sulfur free catalyst steelstrength is no problem.

Accordingly, it is the primary object of the present invention toovercome some of the aforementioned difficulties and provide a means forincreasing the tensile strength and core hardness of sand molds andcores.

It is also an object of the present invention to provide a means forincreasing the working time of sand/resin/catalyst mixes used in theformation of sand molds and cores.

A further object of the present invention is to provide new sulfur-freecatalyst and resin materials for the production of sand molds or coresuseful in providing precision steel castings free of sulfur defects.

Still a further object of our invention is to provide sand molds andcores having enhanced strength and core hardness.

These and other objects of our invention will be more apparent from thediscussion which follows.

SUMMARY OF THE INVENTION

We have found that the working time, tensile strength and core hardnessof sand molds or cores formed from sand particles bound with athermosetting acid-hardenable resin may be increased by adding to amixture of said sand and resin, prior to the curing of the resin, adialkyl ester of the formula:

    R.sub.1 OOC(CH.sub.2).sub.n COOR.sub.2

wherein R₁ and R₂, which may be the same or different, are selected fromalkyl of 1 to 20, preferably 1-12 and most preferably 1 to 4, carbonatoms and n is 2, 3 or 4. The ester may be either blended with the resinor sand, or added in conjunction with an acid catalyst.

A particularly attractive and improved sulfur-free acid catalyst systemaccording to the present invention for the polymerization of athermosetting acid-hardenable resin consists essentially of ferricchloride and a dialkyl ester of the formula:

    R.sub.1 OOC(CH.sub.2).sub.n COOR.sub.2

wherein R₁ and R₂, which may be the same or different, are selected fromalkyl of 1 to 20, preferably 1-12 and most preferably 1 to 4, carbonatoms and n is 2, 3 or 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

According to the present invention the tensile strength and corehardness of a sand mold or core formed by polymerizing a mixture of athermosetting acid-hardenable resin and sand is increased by adding tosaid sand/resin mixture, in an amount sufficient to increase the tensilestrength or core hardness of the polymerized mixture, a dialkyl ester ofthe formula:

    R.sub.1 OOC(CH.sub.2).sub.n COOR.sub.2

wherein R₁ and R₂, which may be the same or different, are selected fromalkyl of 1 to 20, preferably 1 to 12 and most preferably 1 to 4 carbonatoms and n is 2, 3 or 4.

Suitable esters include dimethyl succinate, methylethyl succinate,methyl-n-propyl succinate, methyl isopropyl succinate, methyl-n-butylsuccinate, diethyl succinate, ethyl-n-propyl succinate, diisopropylsuccinate, dibutyl succinate, dimethyl glutarate, methyl-ethylglutarate, methyl-n-propyl glutarate, methyl-isopropyl glutarate,methyl-n-butyl glutarate, methyl-isobutyl glutarate, diethyl glutarate,ethyl-n-propyl glutarate, diisopropyl glutarate, dibutyl glutarate,dimethyl adipate, methyl-ethyl-adipate, methyl-n-propyl adipate,methyl-isopropyl adipate, diethyl adipate, dipropyl adipate and dibutyladipate. Also, one may use dioctyl succinate, dioctyl adipate,octyl-nonyl glutarate, diheptyl glutarate, didecyl dicapryl adipate,dicapryl, succinate, dicapryl glutarate, dilauryl adipate, dilaurylsuccinate and dilauryl glutarate. Preferred esters for use according tothe present invention are dimethyl succinate, dimethyl glutarate anddimethyl adipate with dimethyl glutarate being especially preferred.

The resins employed in forming sand molds or cores are thermosettingacid-hardenable resins well known and conventionally employed in theart. As used herein, the term "thermosetting acid-hardenable resins"refers to any organic material which may be mixed with sand and willcure under acid conditions. Such resins are well known as described forexample in the aforementioned U.S. Pat. Nos. 3,008,205; 3,108,340,3,184,814; British Pat. No. 1,225,984 and Bozer et al, U.S. Pat. No.3,816,375, the entire contents of which is incorporated herein byreference. By way of further illustration, suitable resins includefurfuryl alcohol and its low viscosity (i.e. below 500 centipoise)polymers, furfurylated urea resins, furfuryl alcohol/formaldehyderesins, urea/formaldehyde resins, phenol/formaldehyde resins, furfurylalcohol/phenol/formaldehyde resins, and melamine formaldehyde resins.Preferred resins include those of furfuryl alcohol/formaldehyde,urea/formaldehyde, melamine/formaldehyde, phenol formaldehyde andmixtures thereof. The amount of resin added to the sand must besufficient to bind the sand upon polymerization. Generally, thethermosetting acid-hardenable resin is added in an amount of from about0.5 to 10%, and preferably about 1 to 2% and most suitably about 1.25%by weight, based on the weight of sand.

The acid catalysts suitable for initiating polymerization of thethermosetting acid-hardenable resins are generally well known and aredescribed for example in the aforementioned U.S. Pat. Nos. 3,008,205;3,020,609; 3,108,340; 3,145,438; 3,184,814; 3,639,654; 3,816,375 andAustralian Pat. No. 453,160. The catalyst may be added to the resin orsand/resin mixture in liquid or gaseous form or may be formed in situ.By way of further illustration, but not limited thereto, such materialsas benzene sulfonic acid, toluene sulfonic acid, cumene sulfonic acid,xylene sulfonic acid, sulfuric acid, hydrosulfuric acid, phosphoric acidand such Lewis acids as ferric chloride may be employed as catalysts.Benzene sulfonic acid and toluene sulfonic acid are preferred. However,it should be noted that in some instances it may be desirable to use asulfur-free catalyst particularly where precision steel castings requireno sulfur contamination have a smooth surface are mandatory. In suchinstances a Lewis acid or Bronsted acid catalyst may be used, and apreferred catalyst is ferric chloride, which optionally may be usedtogether with another sulfur-free acid such as hydrochloric acid ornitric acid.

The acid catalyst is added to the resin or resin/sand mixture in anamount sufficient to initiate polymerization of the thermosettingacid-hardenable resin. Generally, from about 15 to 60%, and preferably20 to 30%, by weight of the acid catalyst based on the weight of theresin is sufficient to initiate polymerization.

The dialkyl esters noted above may be incorporated into the sand moldsor cores in a number of ways. If desired, the ester may be blended withthe resin prior to or subsequent to mixing of the resin and sand. Thedialkyl ester may generally be employed in an amount of from about 0.5to 30% and preferably 2.25 to 10% by weight of the thermosettingacid-hardenable resin.

According to another embodiment of the invention, the dialkyl ester maybe incorporated into the catalyst and added therewith to the resin orsand/resin mixture. In such a case, the amount of dialkyl ester added tothe catalyst may suitably range from about 3 to 50% by weight of thecatalyst.

The incorporation of such aliphatic dialkyl esters into sand/resinmixture has been found to increase the tensile strength of the resultingsand mold or cold by as much as 70%.

The following examples are offered in an effort to more fully describethe present invention, but are not to be construed as limiting the scopethereof. In the following examples, all percentages are by weight unlessotherwise noted.

EXAMPLE I

A thermosetting acid-hardenable resin is prepared by mixing and heatingprecooked ureaformaldehyde and furfuryl alcohol together with a mixtureof phenol formaldehyde, furfuryl alcohol and urea. The resin isneutralized with formic acid and 0.1% of a functional silane is added(gammaamino propyltriethoxysilane available from Union Carbide under thedesignation A-1100).

To a number of batches containing 1500 parts standard Ottawa silica sandhaving an AFS fineness in the range 30-120, was added 1.25% of theprepared resin. The sand temperature was about 74° F.

These molding batches were used to prepare cured compositions using thefollowing catalyst compositions:

    ______________________________________                                        Catalyst A                                                                              77.3%     Benzene Sulfonic Acid (90%)                                         12.1%     Water                                                               9.6%      Methanol                                                            1%        HBF.sub.4                                                 Catalyst B                                                                              50.85%    Toluene Sulfonic Acid                                               19.33%    Benzene Sulfonic Acid                                               13.47%    Water                                                               15.00%    Methanol                                                            1.38%     HBF.sub.4                                                 Catalyst C                                                                              100%      Phosphoric Acid (75%)                                     Catalyst D                                                                              70.00%    Toluene Sulfonic Acid                                               30.00%    Methanol -Catalyst E 29% Toluene Sulfonic Acid                      20%       Water                                                               7%        Methanol                                                            33%       Mixture of 52.4% Dimethyl                                                     glutarate, 32% dimethyl                                                       succinate and 15.6%                                                           dimethyl adipate                                                    10%       Sulfuric Acid                                                       1%        HBF.sub.4                                                 Catalyst F                                                                              34.4%     Toluene Sulfonic Acid                                               19.6%     Water                                                               14%       Methanol                                                            22.7%     Mixture of 52.4% Dimethyl                                                     glutarate, 32% dimethyl                                                       succinate and 15.6%                                                           dimethyl adipate                                                    6.9%      Sulfuric Acid                                                       2.6%      HBF.sub.4                                                 Catalyst G                                                                              33%       Toluene Sulfonic Acid                                               33%       Dimethyl Glutarate and                                                        Dimethyl Adipate                                                              (15% / 85% ratio)                                                   15%       Water                                                               5%        Methanol                                                            12.5%     Sulfuric Acid                                                       1.5%      HBF.sub.4                                                 Catalyst H                                                                              33%       Toluene Sulfonic Acid                                               33%       Dimethyl Glutarate                                                  15%       Water                                                               5%        Methanol                                                            12.5%     Sulfuric Acid                                                       1.5%      HBF.sub.4                                                 ______________________________________                                    

Catalyst prepared in accordance with the formulation above was firstmixed with the sand. The quantity of catalyst used will vary from about20% up to about 80% of the weight of resin to be used. The quantity ofcatalyst used is dependent on factors such as the acid demand of thesand, the temperature of the sand and upon the rate of speed of curedesired. Under the sand conditions given above, the quantity of catalystused was 30% by weight of the resin. After thoroughly mulling thecatalyst into the sand, the resin is added thereto and likewise, mulled.After mixing, the sand-resin catalyst mix is placed into a form, tampedor otherwise compacted and allowed to cure.

The set time and tensile strength at 2 and 24 hours was determined ineach case and the results are set forth in Table I below.

EXAMPLE II

A number of acid catalysts were prepared in like manner to those ofExample I above, with the addition of a dialkyl ester in accordance withthe present invention. In each instance, the ester was mixed at roomtemperature with sulfuric acid and allowed to cool. Toluene sulfonicacid and/or benzene sulfonic acid together with water and methanol wasthen added. After mixing, the HBF₄ was added. The catalysts prepared hadthe following compositions:

Catalyst compositions E, F, G and H were blended with the same sandresin mixture and in the same manner and amounts as the catalystcompositions of Example I, and the set time and tensile strengthmeasured. The results are set forth in Table I.

                  TABLE I                                                         ______________________________________                                                          Average      Average                                                Set Time  2 Hour Tensile                                                                             24 Hour Tensile                                Catalyst                                                                              (Minutes) Strength (lbs)                                                                             Strength (lbs)                                 ______________________________________                                        I A     23        310          357                                            I B     28        376          455                                            I C     79        213          504                                            I D     24        319          370                                            II E    38        457          507                                            II F    49        424          446                                            II G    27        430          531                                            II H    27        480          540                                            ______________________________________                                    

EXAMPLE III

Two sulfur-free catalyst compositions were prepared having the followingcompositions:

    ______________________________________                                        Catalyst J   90.5%   FeCl.sub.3                                                            8.0%    HCl                                                                   1.5%    HBF.sub.4                                                Catalyst K   90.5%   Mixture of 92% FeCl.sub.3                                                     and 8% Dimethyl Glutarate                                             8.0%    HCl                                                                   1.5%    HBF.sub.4                                                ______________________________________                                    

The FeCl₃ employed was a sewage grade solution containing 37 to 47%FeCl₃ having up to 0.5 maximum HCl and obtained from Dextrex ChemicalCompany).

Catalyst J was prepared by mixing the ingredients in the proportionsnoted. Since dimethyl glutarate is not readily soluble in FeCl₃,catalyst K was prepared by mixing 92 parts FeCl₃ with 8 parts dimethylglutarate and the mixture heated until 90.5 parts of a miscible solutionresulted the solution was cooled and the HCl and HBF₄ added.

In the same manner as Example I, 25% of catalyst J and K were added tothe resin and the resin was mulled with sand in an amount of 1.25%. Theset time and tensile strength at 2 and 24 hours as well as the scratchhardness at 2 and 24 hours was determined in each case and the resultsset forth in Table II below.

                  TABLE II                                                        ______________________________________                                                       Catalyst J                                                                              Catalyst K                                           ______________________________________                                        Set Time (minutes)                                                                             37          31                                               Average 2 Hour                                                                Tensile Strength (lbs)                                                                         180         266                                              Average 24 Hour                                                               Tensile Strength (lbs)                                                                         155         312                                              Average Scratch                                                               Hardness - 2 Hours                                                                             62          77                                               Average Scratch                                                               Hardness - 24 Hours                                                                            73          81                                               ______________________________________                                    

Other themosetting acid-hardenable resins when used in combination withthe other aliphatic dialkyl esters according to the present inventionshow the same benefits as exemplified above.

The invention in its broader aspects in not limited to the specificdetails shown and described, but departures may be made from suchdetails within the scope of the accompanying claims without departingfrom the principles of the invention.

The invention may furthermore comprise, consist or consist essentiallyof the hereinbefore recited materials and steps.

We claim:
 1. A method for increasing the tensile strength and corehardness of a sand mold or core, said mold or core being formed by acidpolymerizing a mixture of a thermosetting acid-hardenable resin andsand, which comprises, prior to polymerization, adding to and uniformlyblending in said mixture an amount, from 0.5 to 30% by weight of resinsufficient to increase the tensile strength or core hardness of thepolymerized mixture, of a dialkyl ester of the formula:

    R.sub.1 OOC(CH.sub.2).sub.n COOR.sub.2

wherein R₁ and R₂, which may be the same or different, are selected fromalkyl of 1 to 20 carbon atoms and n is 2, 3 or
 4. 2. The method of claim1 wherein R₁ and R₂ are selected from alkyl of 1 to 6 carbon atoms. 3.The method of claim 2 wherein said ester is selected from the groupconsisting of dimethyl succinate, dimethyl glutarate, and dimethyladipate.
 4. The method of claim 1 wherein said resin is selected fromthe group consisting of furfuryl alcohol formaldehyde,urea/formaldehyde, melamine/formaldehyde, phenol/formaldehyde andmixtures thereof.
 5. The method of claim 1 in which said dialkyl esteris added prior to said resin.
 6. The method of claim 1 in which saiddialkyl ester is added simultaneously with said resin.
 7. The method ofclaim 1 in which said dialkyl ester is added in admixture with saidresin.
 8. The method of claim 1 in which said dialkyl ester is addedsubsequent to said resin.
 9. The method of claim 1 in which said dialkylester is added in admixture with a catalyst.
 10. The method of claim 9in which said catalyst is a Lewis or Bronsted acid.